The prior art dealing with catalytic cracking catalysts is voluminous with a basic goal being the preparation of modified zeolites for use as cracking catalysts. The prior art tends to deal with various ways in which the activity and stability of the catalyst may be improved.
It has been disclosed that the steam and thermal stability of zeolites can be improved by the use of zeolites having a low level of alkali metal content and a unit cell size less than about 24.45 Angstroms (See: U.S. Pat. Nos. 3,293,192 and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996)).
Further, it has been disclosed (U.S. Pat. No. 3,591,488) that the hydrogen or ammonium form of a zeolite may be treated with H.sub.2 O at a temperature ranging from about 800.degree. to about 1500.degree. F., and then subsequently cation exchange the steam and water treated zeolite with cations which may be rare earth metal cations. The method increases the silica to alumina mole ratio of the zeolite and also the defect structure.
Another approach taken in an attempt to improve catalytic activity for faujasite-type zeolites is disclosed in U.S. Pat. No. 4,224,188 where the patentee discloses that improved catalytic activity of faujasite-type zeolites can be obtained if the zeolite is first aluminum exchanged and then ammonium exchanged. It is interesting to note that if the ammonium exchange was carried out before the aluminum exchange that no improvement in activity or thermal stability was observed. This is consistent with the publication of K. M. Wang et al. at J. Catal. 24, 262 (1972) which teaches that the hydrogen form of zeolite Y is unstable to hydrothermal treatment when such are aluminum exchanged.
U.S. Pat. No. 4,219,466 purports to disclose that ion-exchange (ammonium, aluminum and rare earth cations) of a silica-alumina hydrogel which contains a zeolite gives a catalyst with improved characteristics. The examples with respect to aluminum exchanged materials show that the aluminum exchange exhibited no improvement as a catalyst.
In copending U.S. Ser. No. 657,417 filed Oct. 3, 1984, there is disclosed improved cracking catalysts derived from Zeolite LZ-210, as disclosed in U.S. Pat. No. 4,503,023 which issued on Mar. 5, 1985. The instant invention relates to Group IIIA ion-exchanged LZ-210 based catalysts.